Silver-containing inorganic antibacterial

ABSTRACT

The present invention provides a silver based inorganic antibacterial agent excellent in heat resistance and chemical resistance, lowered in resin coloring and excellent in processability. The present invention has been completed by finding out that problems can be solved by a silver ion-containing zirconium phosphate represented by the following general formula (1) which is produced by a wet synthesis under specific production conditions.
 
Ag a Na b H c (H 3 O) d Zr e Hf f (PO 4 ) 3   .n H 2 O  (1)
 
wherein, in the formula (1), a, b, c, d, e and f are positive numbers satisfying 1.75&lt;(e+f)&lt;2.25 and a+b+c+d+4(e+f)=9; and n is not more than 2.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a U.S. National Phase entry of International Application No. PCT/JP2007/069562 filed on Oct. 5, 2007, the complete disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a zirconium phosphate carrying a silver ion, and provides a silver based inorganic antibacterial agent excellent in heat resistance, chemical resistance and processability, and also low in coloring when blended with a plastic.

BACKGROUND ART

Recently, zirconium phosphate based inorganic ion exchangers have been utilized in various applications by virtue of their features. Zirconium phosphate based inorganic ion exchangers include amorphous ones, crystalline ones having a two-dimensional layer structure and crystalline ones having a three-dimensional network structure. Above all, hexagonal zirconium phosphates which have a three-dimensional network structure are excellent in heat resistance, chemical resistance and radiation resistance and low in thermal expansion, and are applied to immobilization of radioactive waste, solid electrolytes, gas adsorption/separation agents, catalysts, a raw material for antibacterial agents, and so on.

Hitherto, various hexagonal zirconium phosphates have been known. For example, there are A_(x)NH_(4(1−x))Zr₂(PO₄)₃.nH₂O (for example, refer to Patent Document 1), AZr₂(PO₄)₃.nH₂O (for example, refer to Patent Document 2) and H_(n)R_(1−n)Zr₂(PO₄)₃.mH₂O (for example, refer to Patent Document 3).

Also, zirconium phosphates which differ in a ratio of Zr to P have been known. For example, there are Na_(1+4x)Zr_(2−x)(PO₄)₃ (for example, refer to Non-Patent Document 1), Na_(1+2x)Mg_(x)Zr_(2−x)(PO₄)₃ (for example, refer to Non-Patent Documents 1 and 2) and Na₁₊)Zr₂Si_(x)P_(3−x)O₁₂ (for example, refer to Non-Patent Documents 2 and 3).

As methods for synthesizing these hexagonal zirconium phosphates, have been known a calcining method in which raw materials are mixed, and thereafter calcined at not less than 1000° C. using a calcining furnace to effect the synthesis, a hydrothermal method in which raw materials are mixed in water or in a state of containing water, and thereafter pressurized and heated to effect the synthesis, and a wet method in which raw materials are mixed in water, and thereafter heated at atmospheric pressure to effect the synthesis.

Above all, the calcining method makes it possible to synthesize zirconium phosphates with an appropriately controlled P/Zr ratio just by mixing raw materials and heating them at a high temperature. However, in the calcining method, uniform mixing of raw materials is not easy, and zirconium phosphate with a homogeneous composition is hardly made. Further, the calcining method requires pulverization and classification in order to obtain products in grain form after calcining, and thus it had problems in quality and productivity. Also, as a matter of course, crystalline zirconium phosphates containing ammonia cannot be synthesized in the calcining method. On the other hand, in the wet or hydrothermal method, a homogeneous microparticulate zirconium phosphate can be obtained, but no crystalline zirconium phosphates have been obtained except those having a P/Zr ratio of 1.5 and those indicated by the following formula (4) with a P/Zr ratio of 2. NH₄ZrH(PO₄)₂  (4)

Ions such as of silver, copper, zinc, tin, mercury, lead, iron, cobalt, nickel, manganese, arsenic, antimony, bismuth, barium, cadmium and chromium have been known for a long time as metal ions that indicate antifungal, antibacterial and anti-algae properties (hereinafter, abbreviated to antibacterial metal ions). Especially, silver ion has been widely utilized as an aqueous silver nitrate solution which has effects of disinfection and sterilization. However, metal ions that show the above antifungal, antibacterial or anti-algae property are mostly toxic to human body, and thus there have been various limitations on methods of use, methods of storage, methods of disposing and the like, and applications also have been limited.

In order to exhibit the antifungal, antibacterial or anti-algae property, only a very small amount of antibacterial metal has to be allowed to act on an object of interest. Because of this, as antibacterial agents having the antifungal, antibacterial or anti-algae property, there have been proposed organic carrier based antibacterial agents in which an antibacterial metal ion is carried on an ion exchange resin, a chelate resin or the like, as well as inorganic antibacterial agents in which an antibacterial metal ion is carried on a clay mineral, an inorganic ion exchanger or a porous body.

Of the above various antibacterial agents, inorganic antibacterial agents are characteristic in that they are high in safety, long in durability of antibacterial effect, and also excellent in heat resistance, compared to organic carrier based antibacterial agents.

As one of the inorganic antibacterial agents, has been known an antibacterial agent comprising a clay mineral such as montmorillonite and zeolite in which alkali metal ions such as sodium ion have been ion-exchanged with silver ion. Since it has a skeleton structure based on the clay mineral itself which is inferior in acid resistance, it easily elutes silver ion and thus lacks durability of antibacterial effect, for example, in an acidic solution.

In addition, since the silver ion is unstable upon exposure to heat and light and immediately reduced to a metal silver, thereby causing coloring or the like, it had a problem in long term stability.

There has been one in which silver ion and ammonium ion are co-existent and carried on zeolite by ion exchange in order to enhance the stability of the silver ion. However, even in this case, prevention of coloring does not come to a practical level, and thus no solution has been given fundamentally.

Further, there have been other antibacterial agents in which an antibacterial metal is carried on an adsorptive charcoal. However, since these agents carry soluble antibacterial metal salts which physically adsorb or stick thereto, they rapidly elute antibacterial metal ions and thus lack durability of antibacterial effect when they are brought into contact with moisture.

Recently, an antibacterial agent in which an antibacterial metal ion is carried on a special zirconium phosphate salt has been proposed. For example, one represented by the following formula (5) has been known (for example, refer to Patent Document 4): M¹M² _(x)H_(y)A_(z)(PO₄)₂ .nH₂O  (5) wherein, in the formula (5), M¹ is one selected from tetra-valent metals, M² is one selected from a silver, copper, zinc, tin, mercury, lead, iron, cobalt, nickel, manganese, arsenic, antimony, bismuth, barium, cadmium or chromium, A is one selected from alkali metal ions or alkaline earth metal ions, n is a number satisfying 0≦n≦6, and x, y and z are numbers satisfying 0<(1)X(x)<2, 0<y<2, 0<z<0.5 and (1)X(x)+y+z=2, provided that 1 is the valence number of M².

This antibacterial agent is known as a material which is chemically and physically stable, and shows antifungal and antibacterial properties for a long time. However, when this antibacterial agent is kneaded into a synthetic resin such as nylon, the resin is often colored as a whole and also poor in processability depending upon a particle size so that it cannot be used as a product.

-   Patent Document 1: JP-A-H06-48713 -   Patent document 2: JP-A-H05-17112 -   Patent Document 3: JP-A-S60-239313 -   Patent Document 4: JP-A-H03-83906 -   Non-Patent Document 1: C. JAGER, and three others, “31P and 29 Si     NMR Investigations of the Structure of NASICON-Strukturtyps”,     Expermentelle Technik der Physik, 1988, Vol. 36, 4/5, p 339-348 -   Non-Patent Document 2: C. JAGER, and two others, “31P MAS NMR STUDY     OF THE NASICON SYSTEM Na1+4yZr2-y(PO₄)₃”, Chemical Physics Letters,     1988, Vol. 150, 6, p 503-505 Non-Patent Document 3: H. Y-P. HONG,     “CRYSTAL STRUCTURE AND CRYSTAL CHEMISTRY IN THE SISTEM     Na1+xZr2SixP3-xO12”, Mat. Res. Bull, Vol. 11, p-173-182

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present invention aims at providing a silver based inorganic antibacterial agent excellent in heat resistance and chemical resistance, lowered in resin coloring and excellent in processability.

Means for Solving the Problem

As a result of intensive studies to solve the problem described above, the present inventors have found that the problem can be solved by a zirconium phosphate which contains silver ion, as represented by the general formula (1) shown below: Ag_(a)Na_(b)H_(c)(H₃O)_(d)Zr_(e)Hf_(f)(PO₄)₃ .nH₂O  (1) wherein, in the formula (1), a, b, c, d, e and f are positive numbers satisfying 1.75<(e+f)<2.25 and a+b+c+d+4(e+f)=9; and n is not more than 2.

Therefore, the present invention provides a silver based inorganic antibacterial agent which comprises, as an effective ingredient, a compound represented by the above general formula (1).

In addition, according to a preferable embodiment, there is provided a silver based inorganic antibacterial agent represented by the above general formula (1) which is obtained by allowing a zirconium phosphate represented by the general formula (2) shown below: Ag_(a)Na_(b)H_(c1)Zr_(e)Hf_(f)(PO₄)₃  (2) wherein, in the formula (2), a, b, c1, e and f are positive numbers satisfying 1.75<(e+f)<2.25 and a+b+c1+4(e+f)=9, to absorb moisture.

In addition, according to another preferable embodiment, there is provided a silver based inorganic antibacterial agent represented by the above general formula (1) which is obtained by ion-exchanging a zirconium phosphate compound represented by the general formula (3) shown below: Na_(b1)A_(c1)Zr_(e)Hf_(f)(PO₄)₃ .nH₂O  (3) wherein, in the formula (3), A is ammonium ion and/or hydrogen ion, b1, c1, e and f are positive numbers satisfying 1.75<(e+f)<2.25 and b1+c1+4(e+f)=9, with an aqueous solution containing silver nitrate in an amount of not less than 0.6b1 mol and not more than 0.99b1 mol per 1 mol of the above compound, followed by calcining.

In another aspect, the present invention provides an antibacterial product which contains the silver based inorganic antibacterial agent as defined above.

Effect of the Invention

The present silver based inorganic antibacterial agent is excellent in antibacterial activity and prevention of coloring compared with conventional zirconium phosphate based antibacterial agents.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described. The silver based inorganic antibacterial agent of the present invention is represented by the general formula (1) shown above.

In the formula (1), a is 0<a, preferably not less than 0.01 and more preferably not less than 0.03, and a is preferably not more than 1 and more preferably not more than 0.6. When a is less than 0.01, antibacterial property may not be exhibited sufficiently.

In the formula (1), b is 0<b, and preferably not less than 0.01. Also, b is less than 0.6, preferably less than 0.55, more preferably not more than 0.5 and further more preferably not more than 0.35. When the value of b is large, there is a tendency to cause coloring when the antibacterial agent of the present invention is blended with a resin, and is easy to cause coloring particularly when b is not less than 0.6.

In the formula (1), c is 0<c, preferably not less than 0.01 and more preferably not less than 0.05. Also, c is less than 0.9, preferably less than 0.8 and more preferably not more than 0.7.

In the formula (1), d is 0<d, preferably not less than 0.01, more preferably not less than 0.05 and particularly preferably not less than 0.1. Also, c is less than 0.8, preferably less than 0.7 and more preferably not more than 0.6. When the value of c is less than 0.01 or not less than 0.8, coloring may be easily caused when the antibacterial agent of the present invention is blended with a resin.

In the formula (1), e and f are 1.75<(e+f)<2.25, and e is preferably less than 2.20, more preferably less than 2.15, and preferably not less than 1.80, more preferably not less than 1.85 and further more preferably not less than 1.90. Also, f is preferably not more than 0.2, more preferably not less than 0.001 and not more than 0.15, and more preferably not less than 0.005 and not more than 0.10.

When e+f is not more than 1.75 or not less than 2.25, a homogeneous zirconium phosphate represented by the formula (1) may be difficult to obtain.

In the formula (1), n is preferably not more than 1, more preferably 0.01-0.5 and further preferably 0.03-0.3. When n exceeds 2, the silver based inorganic antibacterial agent of the present invention contains a large absolute amount of moisture, and thus may cause foaming, hydrolysis or the like during processing and the like.

The followings can be illustrated as the silver based inorganic antibacterial agents represented by the formula (1).

Ag_(0.05)Na_(0.02)H_(0.3)(H₃O)_(0.55)Zr_(2.0)Hf_(0.02)(PO₄)₃.0.15H₂O

Ag_(0.10)Na_(0.02)H_(0.25)(H₃O)_(0.40)Zr_(2.01)Hf_(0.03)(PO₄)₃.0.10H₂O

Ag_(0.17)Na_(0.02)H_(0.35)(H₃O)_(0.30)Zr_(2.03)Hf_(0.01)(PO₄)₃.0.05H₂O

Ag_(0.17)Na_(0.04)H_(0.2)(H₃O)_(0.55)Zr_(1.99)Hf_(0.02)(PO₄)₃.0.25H₂O

Ag_(0.17)Na_(0.10)H_(0.3)(H₃O)_(0.45)Zr_(1.92)Hf_(0.15)(PO₄)₃.0.15H₂O

Ag_(0.17)Na_(0.12)H_(0.2)(H₃O)_(0.35)Zr_(1.92)Hf_(0.05)(PO₄)₃.0.15H₂O

Ag_(0.45)Na_(0.12)H_(0.2)(H₃O)_(0.35)Zr_(1.95)Hf_(0.02)(PO₄)₃.0.05H₂O

Ag_(0.55)Na_(0.15)H_(0.4)(H₃O)_(0.45)Zr_(1.99)Hf_(0.01)(PO₄)₃.0.15H₂O

Ag_(0.55)Na_(0.05)H_(0.20)(H₃O)_(0.35)Zr_(1.98)Hf_(0.02)(PO₄)₃.0.2H₂O

Ag_(0.39)Na_(0.11)H_(0.21)(H₃O)_(0.59)Zr_(1.91)Hf_(0.015)(PO₄)₃.0.19H₂O

Ag_(0.18)Na_(0.07)H_(0.11)(H₃O)_(0.33)Zr_(1.93)Hf_(0.02)(PO₄)₃.0.27H₂O

Ag_(0.2)Na_(0.05)H_(0.20)(H₃O)_(0.40)Zr_(1.91)Hf_(0.02)(PO₄)₃.0.22H₂O

The silver based inorganic antibacterial agent of the present invention defined in the above formula (1) can be obtained by allowing a compound represented by the formula (2) shown below to absorb moisture. Ag_(a)Na_(b)H_(c1)Zr_(e)Hf_(f)(PO₄)₃  (2) wherein, in the formula (2), a, b, c1, e and f are positive numbers satisfying 1.75<(e+f)<2.25 and a+b+c1+4(e+f)=9.

A method for allowing a zirconium phosphate compound represented by the formula (2) to absorb moisture can be performed by leaving the zirconium phosphate compound represented by the formula (2) to stand still or to be stirred in an atmosphere at a temperature of less than 220° C. and preferably not more than 200° C. and a humidity of not less than 20% and preferably under normal pressure. Time for leaving it to stand still or to be stirred must be not less than 10 minutes, preferably not less than an hour and more preferably not less than 3 hours. When the atmospheric temperature is not less than 220° C. or the atmospheric humidity is less than 20%, rate of moisture absorption becomes slow, and thus long treatment time is required.

Although the absorbed moisture partly exists as a crystal water, it is consumed for conversion of hydrogen ion to oxonium ion according to the amount of the hydrogen ion contained in the zirconium phosphate. Distinction of hydrogen ion and oxonium ion can be confirmed by the decrease in the vibration peak of infrared absorption spectrum at 820 cm⁻ caused by hydrogen ion.

The followings can be illustrated as the silver based inorganic antibacterial agents represented by the formula (2).

Ag_(0.05)Na_(0.02)H_(0.85)Zr_(2.0)Hf_(0.02)(PO₄)₃

Ag_(0.10)Na_(0.02)H_(0.65)Zr_(2.01)Hf_(0.03)(PO₄)₃

Ag_(0.17)Na_(0.02)H_(0.65)Zr_(2.03)Hf_(0.01)(PO₄)₃

Ag_(0.17)Na_(0.04)H_(0.75)Zr_(1.99)Hf_(0.02)(PO₄)₃

Ag_(0.17)Na_(0.10)H_(0.75)Zr_(1.92)Hf_(0.15)(PO₄)₃

Ag_(0.17)Na_(0.12)H_(0.55)Zr_(1.92)Hf_(0.05)(PO₄)₃

Ag_(0.45)Na_(0.12)H_(0.55)Zr_(1.95)Hf_(0.02)(PO₄)₃

Ag_(0.55)Na_(0.15)H_(0.85)Zr_(1.99)Hf_(0.01)(PO₄)₃

Ag_(0.55)Na_(0.05)H_(0.55)Zr_(1.98)Hf_(0.02)(PO₄)₃

Ag_(0.39)Na_(0.11)H_(0.8)Zr_(1.91)Hf_(0.015)(PO₄)₃

Ag_(0.18)Na_(0.07)H_(0.34)Zr_(1.93)Hf_(0.02)(PO₄)₃

Ag_(0.2)Na_(0.05)H_(0.6)Zr_(1.91)Hf_(0.015)(PO₄)₃

In addition, the silver based inorganic antibacterial agent of the present invention represented by the formula (2) can be obtained by ion-exchanging a zirconium phosphate compound represented by the formula (3) shown below with a solution containing silver nitrate in an amount of not less than 0.6b1 mol and not more than 0.99b1 mol per 1 mol of the zirconium phosphate compound, followed by calcining. Na_(b1)A_(c1)Zr_(e)Hf_(f)(PO₄)₃ .nH₂O  (3) wherein, in the formula (3), A is ammonium ion and/or hydrogen ion, b1, c1, e and f are positive numbers satisfying 1.75<(e+f)<2.25 and b1+c1+4(e+f)=9.

The method for synthesizing the zirconium phosphate represented by the formula (3) includes wet methods or hydrothermal methods in which various raw materials are reacted in an aqueous solution. Examples of concrete synthesis methods of a zirconium phosphate represented by the formula (3) in which A is ammonium ion include a synthesis method in which an aqueous solution containing predetermined amounts of a zirconium compound, ammonia or a salt thereof, oxalic acid or a salt thereof and phosphoric acid or a salt thereof is adjusted to a pH of not more than 4 with caustic soda or aqueous ammonia, and then is heated at a temperature of not less than 70° C. Also, examples of concrete synthesis methods of a zirconium phosphate represented by the formula (3) in which A is hydrogen ion include a synthesis method in which an aqueous solution containing predetermined amounts of a zirconium compound, oxalic acid or a salt thereof and phosphoric acid or a salt thereof is adjusted to a pH of not more than 4 with caustic soda, and then is heated at a temperature of not less than 70° C. to produce a zirconium phosphate, followed by further stirring in an aqueous solution of hydrochloric acid, nitric acid or sulfuric acid so as to carry hydrogen ion thereon. Meanwhile, the step for carrying hydrogen ion can be conducted at the same time when silver ion is carried using silver nitrate or after the silver ion has been carried. The zirconium phosphate that has been synthesized is further filtrated, washed well with water, dried and then lightly pulverized to obtain white microparticulate zirconium phosphate. In addition, in case of the hydrothermal method in which synthesis is conducted at a temperature exceeding 100° C. under pressure, the zirconium phosphate represented by the formula (3) can be synthesized without use of oxalic acid or a salt thereof.

The zirconium compound which can be used as raw materials for the zirconium phosphate represented by the formula (3) includes a water-soluble or acid-soluble zirconium salt. Examples of these zirconium salts include zirconium nitrate, zirconium acetate, zirconium sulfate, zirconium basic sulfate, zirconium oxysulfate and zirconium oxychloride, and in consideration of reactivity and economy, zirconium oxychloride is preferable.

Hafnium compounds usable as a raw material for synthesis of the zirconium phosphate represented by the formula (3) are water-soluble or acid-soluble hafnium salt. These hafnium salts are exemplified by hafnium chloride, hafnium oxychloride, hafnium ethoxide and the like, and a zirconium compound containing hafnium can also be used. A content of hafnium in the zirconium compound is preferably not less than 0.1% and not more than 5%, and more preferably not less than 0.3% and not more than 4%. In the present invention, it is preferred that zirconium oxychloride containing hafnium in such a small amount as mentioned above is used, taking in consideration of reactivity and economy.

Oxalic acid or a salt thereof usable as a raw material for synthesis of the zirconium phosphate represented by the formula (3) are exemplified by oxalic acid dihydrate, sodium oxalate, ammonium oxalate, sodium hydrogen oxalate and ammonium hydrogen oxalate, and preferably oxalic acid dihydrate.

Ammonia or a salt thereof usable as a raw material for synthesis of the zirconium phosphate represented by the formula (3) are exemplified by ammonium chloride, ammonium nitrate, ammonium sulfate, aqueous ammonia, ammonium oxalate, and ammonium phosphate, and preferably ammonium chloride or aqueous ammonia.

Phosphoric acid or a salt thereof usable as a raw material for synthesis of the zirconium phosphate represented by the formula (3) are preferably a soluble or acid-soluble salt which is exemplified by phosphoric acid, sodium phosphate, sodium hydrogenphosphate and ammonium hydrogenphosphate and ammonium phosphate, and more preferably phosphoric acid. Meanwhile, the concentration of the phosphoric acid is preferably about 60-85%.

Upon synthesis of the zirconium phosphate represented by the formula (3), a molar ratio of the phosphoric acid or a salt thereof to the zirconium compound (assuming that the zirconium compound is 1) is usually more than 1.5 and less than 2, more preferably 1.51 to less than 1.71, further more preferably 1.52-1.67, and particularly preferably 1.52-1.65.

That is, a preferable synthesis method of the zirconium phosphate represented by the formula (3) is a wet method or hydrothermal method in which the molar amount of phosphoric acid or salt thereof per 1 mole of zirconium compound is in a range between more than 1.3 and less than 2.

Upon synthesis of the zirconium phosphate represented by the formula (3), a molar ratio of phosphoric acid or salt thereof to ammonia or salt thereof (assuming that ammonia or salt thereof is 1) is preferably 0.3-10, further more preferably 1-10 and particularly preferably 2-5.

That is, a preferable synthesis method of the zirconium phosphate represented by the formula (3) is a wet method or hydrothermal method with ammonia or a salt thereof.

Upon synthesis of the zirconium phosphate represented by the formula (3), a molar ratio of phosphoric acid or salt thereof to oxalic acid or salt thereof (assuming that oxalic acid or salt thereof is 1) is preferably 1-6, more preferably 1.5-5, further more preferably 1.51-4 and particularly preferably 1.52-3.5.

That is, a preferable synthesis method of the zirconium phosphate represented by the formula (3) is a wet method or hydrothermal method with oxalic acid or a salt thereof. However, in case of a hydrothermal method, it is not required to contain oxalic acid or a salt thereof.

The solid content in a reaction slurry for synthesis of the zirconium phosphate represented by the formula (3) is preferably 3 wt % or more, and in consideration of efficiency such as economy, more preferably 7-15%.

The pH upon synthesis of the zirconium phosphate represented by the formula (3) is preferably not less than 1 and not more than 4, more preferably 1.3-3.5, further more preferably 1.8-3.0 and particularly preferably 2.0-3.0. When the pH exceeds 4, the zirconium phosphate represented by the formula (3) may not be synthesized. When the pH is less than 1, the zirconium phosphate represented by the formula (3) may not be synthesized. For the adjustment of the pH, sodium hydroxide, potassium hydroxide or aqueous ammonia is preferably used, and more preferably sodium hydroxide is used.

The temperature upon synthesis of the zirconium phosphate represented by the formula (3) is preferably not less than 70° C., more preferably not less than 80° C., further more preferably not less than 90° C. and particularly preferably not less than 95° C. Also, as the synthesis temperature, a temperature of not more than 150° C. is preferable and not more than 120° C. is more preferable. When the temperature is less than 70° C., the zirconium phosphate of the present invention may not be synthesized. When the temperature exceeds 150° C., the synthesis is energetically disadvantageous.

When the zirconium phosphate represented by the formula (3) is synthesized, it is desirable that the raw materials are homogeneously mixed and stirred so as to effect the reaction to uniformly proceed.

The time for synthesizing the zirconium phosphate represented by the formula (3) differs depending upon the synthesis temperature. For example, the time for synthesizing the zirconium phosphate of the present invention is preferably not less than 4 hours, more preferably 8-72 hours and further more preferably 10-48 hours.

The zirconium phosphate represented by the formula (3) can be synthesized as a compound with a median diameter of 0.1-5 μm. The median diameter of the zirconium phosphate represented by the formula (3) is preferably 0.1-5 μm, more preferably 0.2-3 μm and further more preferably 0.3-2 μm. Meanwhile, in consideration of processability into various products, in addition to the median diameter, the maximum particle diameter is also important. Therefore, the maximum particle diameter of the zirconium phosphate represented by the formula (3) is preferably not more than 10 μm, further preferably not more than 8 μm and particularly preferably not more than 6 μm from the viewpoint of the effect.

As the zirconium phosphate represented by the formula (3) which can be used as a raw material of the silver based inorganic antibacterial agent of the present invention, the followings can be exemplified.

Na_(0.07)(NH₄)_(0.85)Zr_(2.0)Hf_(0.02)(PO₄)₃.0.65H₂O

Na_(0.12)(NH₄)_(0.65)Zr_(2.01)Hf_(0.03)(PO₄)₃.0.85H₂O

Na_(0.19)(NH₄)_(0.65)Zr_(2.03)Hf_(0.01)(PO₄)₃.0.75H₂O

Na_(0.21)(NH₄)_(0.75)Zr_(1.99)Hf_(0.02)(PO₄)₃.0.6H₂O

Na_(0.27)(NH₄)_(0.75)Zr_(1.92)Hf_(0.15)(PO₄)₃.0.75H₂O

Na_(0.29)(NH₄)_(0.55)Zr_(1.92)Hf_(0.05)(PO₄)₃.0.5H₂O

Na_(0.57)(NH₄)_(0.55)Zr_(1.95)Hf_(0.02)(PO₄)₃.0.35H₂O

Na_(0.70)(NH₄)_(0.85)Zr_(1.99)Hf_(0.01)(PO₄)₃.0.4H₂O

Na_(0.07)H_(0.85)Zr_(2.0)Hf_(0.02)(PO₄)₃.0.65H₂O

Na_(0.12)H_(0.65)Zr_(2.01)Hf_(0.03)(PO₄)₃.0.85H₂O

Na_(0.19)H_(0.65)Zr_(2.03)Hf_(0.01)(PO₄)₃.0.75H₂O

Na_(0.21)H_(0.75)Zr_(1.99)Hf_(0.02)(PO₄)₃.0.6H₂O

Na_(0.27)H_(0.75)Zr_(1.92)Hf_(0.15)(PO₄)₃.0.75H₂O

Na_(0.29)H_(0.55)Zr_(1.92)Hf_(0.05)(PO₄)₃.0.5H₂O

Na_(0.57)H_(0.55)Zr_(1.95)Hf_(0.02)(PO₄)₃.0.35H₂O

Na_(0.70)H_(0.85)Zr_(1.99)Hf_(0.01)(PO₄)₃.0.4H₂O

Na_(0.6)(NH₄)_(0.4)Zr_(1.98)Hf_(0.02)(PO₄)₃.0.09H₂O

Na_(0.5)(NH₄)_(0.8)Zr_(1.91)Hf_(0.015)(PO₄)₃.0.11H₂O

Na_(0.25)(NH₄)_(0.95)Zr_(1.93)Hf_(0.02)(PO₄)₃.0.09H₂O

Na_(0.25)H_(0.6)Zr_(1.91)Hf_(0.015) (PO₄)₃.0.37H₂O

The compound of the formula (2) can be obtained by ion-exchanging the zirconium phosphate represented by the formula (3) with silver ion, and then calcining. The method for silver ion-exchanging can be conducted by immersing the zirconium phosphate represented by the formula (3) in an aqueous solution containing silver nitrate of not less than 0.6b1 mol and not more than 0.99b1 mol, and preferably not less than 0.7b1 mol and not more than 0.98b1 mol per 1 mol of the zirconium phosphate compound. When the content of the silver nitrate is not more than 0.6b1 mol, coloring is increased when it is blended with a resin. On the other hand, when it is not less than 0.99b1 mol, the silver nitrate may not be completely used so as to remain non-ion-exchanged in the ion-exchanged solution, and thus it is not economical. Also, when the immersion is conducted, it is preferable to provide a condition under which they are uniformly mixed by stirring or the like. The amount to be immersed only has to meet a concentration at which uniform mixing with the aqueous solution can be conducted. For this purpose, the concentration of the zirconium phosphate represented by the formula (3) is preferably not more than 20 weight %.

In order to prepare the aqueous solution containing a silver ion, it is preferable to use an aqueous solution which is made by dissolving silver nitrate in ion exchanged water. The temperature of the aqueous solution during ion exchange is usually 0-100° C. and preferably 20-80° C. Since the ion exchange proceeds immediately, the time for immersion may be not more than 5 minutes, but is preferably from 30 minutes to 5 hours in order to attain a high silver ion conversion uniformly. The silver ion exchange will not proceed further if the time for immersion is extended to 5 hours or more.

After the completion of the silver ion exchange, the reaction product is well washed with ion exchange water and the like, and then calcined to obtain a compound represented by the formula (2).

The calcining temperature is preferably 550-1000° C., more preferably 600-900° C., and further more preferably 650-800° C. for improvement of colorlessness. Also, the time for calcining is preferably not less than 1 hour, more preferably not less than 2 hours, and further more preferably not less than 3 hours for improvement of colorlessness. The time for calcining is preferably not more than 48 hours and further preferably not more than 36 hours. Since particles of the silver based inorganic antibacterial agent of the present invention may sometimes be aggregated after calcined, aggregated one should be pulverized using a pulverizer.

The form of use of the silver based inorganic antibacterial agent of the present invention is not particularly limited, and it can be appropriately mixed with another component or can be combined with another material according to use. For example, it can be used in various forms including powder, powder-containing dispersion, powder-containing particle, powder-containing paint, powder-containing fiber, powder-containing paper, powder-containing plastic, powder-containing film and powder-containing aerosol. Further, it can be used in combination with various additive agents or materials such as deodorant, fire-extinguishing agent, anti-corrosive agent, fertilizer and building materials, as required.

The silver based inorganic antibacterial agent of the present invention can be mixed with various additives if required, in order to improve processability for kneading into the resin and other properties. Concrete examples thereof include pigments such as zinc oxide and titanium oxide, inorganic ion exchangers such as zirconium phosphate and zeolite, dyes, antioxidants, light stabilizers, flame retardants, antistatic agents, foaming agents, impact resistance reinforcements, glass fibers, lubricants such as metal soap, desiccants, expanders, coupling agents, nucleators, fluidity improvers, deodorants, wood powder, anti-fungal agents, antifouling agents, rust preventives, metal powder, ultraviolet absorbers, and ultraviolet screeners.

The antibacterial resin composition can easily be obtained by blending the silver based inorganic antibacterial agent of the present invention with a resin. A kind of resin which can be used is not particularly limited, and is any of natural resins, synthetic resins and semi-synthetic resins, and also any of thermoplastic resins and thermosetting resins. Concrete resins may be any of resins for molding, resins for fiber or rubbery resins, including, for example, resins for molding or fiber such as polyethylene, polypropylene, vinyl chloride, ABS resin, AS resin, MBS resin, nylon resin, polyester, polyvinylidene chloride, polystyrene, polyacetal, polycarbonate, PBT, acrylic resin, fluorocarbon polymer, polyurethane elastomer, polyester elastomer, melamine, urea resin, polytetrafluoroethylene resin, unsaturated polyester resin, rayon, acetate, acryl, polyvinyl alcohol, cupra, triacetate and vinylidene; and rubbery resins such as natural rubber, silicone rubber, styrene butadiene rubber, ethylene propylene rubber, fluoro rubber, nitrile rubber, chlorosulfonated polyethylene rubber, butadiene rubber, synthetic natural rubber, butyl rubber, urethane rubber and acrylic rubber. In addition, antibacterial fiber can be produced by combining the silver based inorganic antibacterial agent of the present invention with a fiber of natural fibers.

The blending proportion of the silver based inorganic antibacterial agent of the present invention in the above antibacterial resin composition is preferably 0.03-5 parts by weight and more preferably 0.1-2.0 parts by weight based on 100 parts by weight of the antibacterial resin composition. When the proportion is less than 0.03 part by weight, antibacterial property of the antibacterial resin composition may be insufficient. On the other hand, when the proportion is more than 5 parts by weight, further improvement of antibacterial effect is hardly expected, and thus it is uneconomical and may considerably lower the properties of resin.

As a method of blending the silver based inorganic antibacterial agent of the present invention with a resin to make a resin molded article, the conventional methods can be adopted. Examples thereof are (1) a method in which a pellet resin or powder resin is directly mixed in a mixer using an impregnation agent for facilitating attachment of the silver based inorganic antibacterial agent powder to a resin or dispersing agent for improving dispersibility of the antibacterial agent powder, (2) a method in which mixing is conducted as described in the above method, followed by molding the mixture into a pellet form in an extrusion-molding machine, and then the molded product is blended with a pellet resin, (3) a method in which the silver based inorganic antibacterial agent is molded into a highly concentrated pellet form using a wax, and then the pelletized molded product is blended with a pellet resin, and (4) a method in which a paste composition is prepared by dispersing and mixing the silver based inorganic antibacterial agent in a highly viscous liquid such as a polyol, and then the paste is blended with a pellet resin.

For molding the above antibacterial resin composition, various conventional processing techniques and machines can be used according to characteristics of various resins. That is, it can be molded easily by means of mixing, mingling or kneading at an appropriate temperature or pressure, for example, under heating and pressurizing or depressurizing. Their specific operations only have to follow the ordinary methods, so as to mold and process into various forms such as lump form, sponge form, film form, sheet form, thread form, pipe form or combination of these.

The form of use of the silver based inorganic antibacterial agent of the present invention is not particularly limited, and is not limited to blending with a resin molded product or polymer compound. It can be properly mixed with other components or combined with other materials in accordance with uses that require antifungal, anti-algae and antibacterial properties. For example, it can be used in various forms such as powder form, powder dispersion form, granular form, aerosol form, or liquid form.

Uses

The silver based inorganic antibacterial agent of the present invention can be used in various fields which require antifungal, anti-algae and antibacterial properties, that is, electrical products, kitchen products, fiber products, house or building material products, toiletry products, paper products, toys, leather products, stationery and other products.

Further, concrete applications are exemplified by electrical products such as dishwashers, dishdryers, refrigerators, washing machines, pots, televisions, personal computers, radio cassette recorders, cameras, video cameras, water purifiers, rice cookers, vegetable cutters, registers, bedding dryers, fax machines, ventilating fans, and air conditioners; and kitchen products such as dishes, cutting boards, cutters, trays, chopsticks, teapots, thermos bottles, knives, grips of ladles, spatulas, lunch boxes, rice scoops, bowls, strainer baskets, triangle corners, scourer cases, rubbish baskets and strainer bags.

Examples of fiber products are shower curtains, bedding cottons, air conditioner filters, panty hoses, socks, small damp towels, bed sheets, bedding covers, pillow, gloves, aprons, curtains, nappies, bandages, masks and sport wear; and examples of house or building material products are decorative boards, wall paper, floor boards, films for window, handles, lags, mats, artificial marbles, handrails, joints, tiles and waxes. Examples of toiletry products are toilet seats, bathtubs, tiles, bedpans, dirt cases, toilet brushes, bath covers, pumice, soap cases, bath chairs, cloth basket, showers and washstands; examples of paper products are wrapping paper, drug packing paper, medicine chests, sketchbooks, medical records, notebooks and origamis; and examples of doll, stuffed toys, paper clays, blocks and puzzles.

Further, examples of leather products are shoes, bags, belts, watch bands, interior equipment, chairs, gloves and straps; and examples of stationery are ballpoint pens, mechanical pens, pencils, erasers, crayons, paper, diaries, flexible disks, rulers, post-it and staplers.

Examples of other products are insoles, cosmetic containers, scourers, powder puffs, hearing aids, musical instruments, cigarette filters, adhesive paper sheets for cleaning, strap grips, sponges, kitchen towels, cards, microphones, barbar tools, vender machines, shavers, telephones, thermometers, stethoscopes, slippers, clothes cases, teeth brushes, sand for sandpits, food wrapping films, antibacterial sprays and paints.

EXAMPLE

Hereinafter, the present invention will be described in detail by way of working examples. However, the present invention is not limited to these.

The median diameter and maximum particle diameter were measured by using a laser diffraction particle analyzer on volume basis.

The amount of zirconium was calculated by dissolving a sample using a strong acid, and then measuring the resulting liquid by an ICP emission spectrometer. The amount of phosphorus was calculated by dissolving a sample using a strong acid, and then measuring the resulting liquid by an ICP emission spectrometer. The amount of sodium was calculated by dissolving a sample using a strong acid, and then measuring the resulting liquid by an atomic absorption spectrometer. The amount of ammonia was calculated by dissolving a sample using a strong acid, and then measuring the resulting liquid by indophenol method. The amount of oxonium ion was calculated by measuring the amount of weight loss by a thermal analysis at 160-190° C.

Example 1

0.1 mol of oxalic acid dihydrate, 0.2 mol of zirconium oxychloride octahydrate containing 0.18% hafnium and 0.1 mol of ammonium chloride were dissolved in 300 ml of deionized water, and then 0.3 mol of phosphoric acid was added thereto under stirring. A 20% aqueous sodium hydroxide solution was added to the solution to adjust the pH to 2.7, and then stirred at 98° C. for 14 hours. Then, the resulting precipitates were washed well, and dried at 120° C. to synthesize a zirconium phosphate compound.

As a result of measurement of the amount of each component of the zirconium phosphate, the compositional formula was found as follows:

Na_(0.6)(NH₄)_(0.4)Zr_(1.98)Hf_(0.02)(PO₄)₃.0.09H₂O.

To 0.09 mol of the resulting zirconium phosphate, a solution of 0.05 mol of silver nitrate (Ag/Na=0.93) in 450 ml of ion-exchanged water was added, and stirred at 60° C. for 2 hours to carry a silver ion. Then, it was washed well, dried at 120° C. and calcined at 650° C. for 4 hours.

As a result of measurement of the amount of each component of the zirconium phosphate, the compositional formula was found as follows:

Ag_(0.55)Na_(0.05)H_(0.55)Zr_(1.98)Hf_(0.02)(PO₄)₃.

The calcined powder was lightly pulverized, and then was left to stand for 6 hours under an atmospheric humidity of 40% and temperature of 55° C. so as to effect a treatment for moisture absorption, to obtain a silver based inorganic antibacterial agent of the present invention. As a result of measurement of the amount of each component of the silver based inorganic antibacterial agent, the compositional formula was found as follows:

Ag_(0.55)Na_(0.05)H_(0.20)(H₃O)_(0.35)Zr_(1.98)Hf_(0.02)(PO₄)₃.0.2H₂O.

Median diameter (μm), maximum particle diameter (μm) and minimum inhibitory concentration (MIC, μg/ml) against Escherichia coli of the silver based inorganic antibacterial agent were measured, and these results are shown in Table 1.

Example 2

0.1 mol of oxalic acid dihydrate, 0.19 mol of zirconium oxychloride octahydrate containing 0.18% hafnium and 0.10 mol of ammonium chloride were dissolved in 300 ml of deionized water, and then 0.3 mol of phosphoric acid was added thereto under stirring. A 20% aqueous sodium hydroxide solution was added to the solution to adjust the pH to 2.7, and then stirred at 98° C. for 14 hours. Then, the resulting precipitates were washed well, and dried at 120° C. to synthesize a zirconium phosphate compound.

As a result of measurement of the amount of each component of the zirconium phosphate, the compositional formula was found as follows:

Na_(0.5)(NH₄)_(0.8)Zr_(1.91)Hf_(0.015)(PO₄)₃.0.11H₂O.

To 0.09 mol of the resulting zirconium phosphate, a solution of 0.035 mol of silver nitrate (Ag/Na=0.78) in 450 ml of 1N nitric acid solution was added, and stirred at 60° C. for 2 hours to carry a silver ion. Then, it was washed well, dried at 120° C. and then calcined at 720° C. for 4 hours.

As a result of measurement of the composition of the zirconium phosphate, the compositional formula was found as follows:

Ag_(0.39)Na_(0.11)H_(0.8)Zr_(1.91)Hf_(0.015)(PO₄)₃.

The calcined powder was lightly pulverized, and then was left to stand for 6 hours under an atmospheric humidity of 50% and temperature of 110° C. so as to effect a treatment for moisture absorption, to obtain a silver based inorganic antibacterial agent of the present invention. As a result of measurement of the amount of each component of the silver based inorganic antibacterial agent, the compositional formula was found as follows:

Ag_(0.39)Na_(0.11)H_(0.21)(H₃O)_(0.59)Zr_(1.91)Hf_(0.015)(PO₄)₃.0.19H₂O.

Median diameter (μm), maximum particle diameter (μm) and minimum inhibitory concentration (MIC, μg/ml) against Escherichia coli of the silver based inorganic antibacterial agent were measured, and these results are shown in Table 1.

Example 3

0.195 mol of zirconium oxychloride octahydrate containing 0.18% hafnium and 0.12 mol of ammonium chloride were dissolved in 300 ml of deionized water, and then 0.3 mol of phosphoric acid was added thereto under stirring. A 20% aqueous sodium hydroxide solution was added to the solution to adjust the pH to 2.7, and then stirred at 140° C. under saturated vapor pressure for 4 hours. Then, the resulting precipitates were washed well, and dried at 120° C. to synthesize a zirconium phosphate compound.

As a result of measurement of the amount of each component of the zirconium phosphate, the compositional formula was found as follows:

Na_(0.25)(NH₄)_(0.95)Zr_(1.93)Hf_(0.02)(PO₄)₃.0.09H₂O.

To 0.09 mol of the resulting zirconium phosphate, a solution of 0.018 mol of silver nitrate in 450 ml of ion-exchanged water was added, and stirred at 60° C. for 2 hours to carry a silver ion. Then, it was washed well, dried at 120° C. and calcined at 700° C. for 4 hours.

As a result of measurement of the amount of each component of the zirconium phosphate, the compositional formula was found as follows:

Ag_(0.18)Na_(0.07)H_(0.34)Zr_(1.93)Hf_(0.02)(PO₄)₃.

The calcined powder was lightly pulverized, and then was left to stand for 24 hours under an atmospheric humidity of 50% and temperature of 35° C. so as to effect a treatment for moisture absorption, to obtain a silver based inorganic antibacterial agent of the present invention. As a result of measurement of the amount of each component of the silver based inorganic antibacterial agent, the compositional formula was found as follows:

Ag_(0.18)Na_(0.07)H_(0.11)(H₃O)_(0.33)Zr_(1.93)Hf_(0.02)(PO₄)₃.0.27H₂O.

Median diameter (μm), maximum particle diameter (μm) and minimum inhibitory concentration (MIC, μg/ml) against Escherichia coli of the silver based inorganic antibacterial agent were measured, and these results are shown in Table 1.

Example 4

0.1 mol of oxalic acid dihydrate and 0.193 mol of zirconium oxychloride octahydrate containing 0.18% hafnium were dissolved in 300 ml of deionized water, and then 0.3 mol of phosphoric acid was added thereto under stirring. A 20% aqueous sodium hydroxide solution was added to the solution to adjust the pH to 2.9, and then stirred at 98° C. for 14 hours. Then, the resulting precipitates were washed well, ion-exchanged using a 1N nitric acid solution and dried at 120° C. to synthesize a zirconium phosphate.

As a result of measurement of the amount of each component of the zirconium phosphate, the compositional formula was found as follows:

Na_(0.25)H_(0.6)Zr_(1.91)Hf_(0.015)(PO₄)₃.0.37H₂O.

To 0.09 mol of the resulting zirconium phosphate, a solution of 0.018 mol of silver nitrate (Ag/Na=0.8) in 450 ml of a 1N nitric acid solution was added, and stirred at 60° C. for 2 hours to carry a silver ion. Then, it was washed well, dried at 120° C. and calcined at 700° C. for 4 hours.

As a result of measurement of the amount of each component of the zirconium phosphate, the compositional formula was found as follows:

Ag_(0.2)Na_(0.05)H_(0.6)Zr_(1.91)Hf_(0.015)(PO₄)₃.

The calcined powder was lightly pulverized, and then was left to stand for 24 hours under an atmospheric humidity of 50% and temperature of 35° C. so as to effect a treatment for moisture absorption, to obtain a silver based inorganic antibacterial agent of the present invention. As a result of measurement of the amount of each component of the silver based inorganic antibacterial agent, the compositional formula was found as follows:

Ag_(0.2)Na_(0.05)H_(0.20)(H₃O)_(0.40)Zr_(1.91)Hf_(0.02)(PO₄)₃.0.22H₂O.

Median diameter (μm), maximum particle diameter (μm) and minimum inhibitory concentration (MIC, μg/ml) against Escherichia coli of the silver based inorganic antibacterial agent were measured, and these results are shown in Table 1.

Comparative Example 1

A comparative silver based inorganic antibacterial agent was obtained by the same procedures as in Example 3 except that the treatment for moisture absorption was not performed. The compositional formula of this comparative silver based inorganic antibacterial agent was as follows:

Ag_(0.18)Na_(0.07)H_(0.34)Zr_(1.93)Hf_(0.02)(PO₄)₃.

Median diameter (μm), maximum particle diameter (μm) and minimum inhibitory concentration (MIC, μg/ml) against Escherichia coli of the comparative silver based inorganic antibacterial agent were measured, and these results are shown in Table 1.

Comparative Example 2

A comparative silver based inorganic antibacterial agent was obtained by the same procedures as in Example 3 except that calcining was not performed. The compositional formula of this comparative silver based inorganic antibacterial agent was:

Ag_(0.18)Na_(0.07)(NH₄)_(0.34)Zr_(1.93)Hf_(0.02)(PO₄)₃.0.43H₂O.

Median diameter (μm), maximum particle diameter (μm) and minimum inhibitory concentration (MIC, μg/ml) against Escherichia coli of the comparative silver based inorganic antibacterial agent were measured, and these results are shown in Table 1.

Comparative Example 3

A comparative silver based inorganic antibacterial agent was obtained by the same procedures as in Example 2 except that an ion exchanged water in which 0.015 mol (Ag/Na=0.33) of silver nitrate was dissolved was used to carry the silver. The compositional formula of this comparative silver based inorganic antibacterial agent was:

Ag_(0.16)Na_(0.34)H_(0.24)(H₃O)_(0.56)Zr_(1.91)Hf_(0.015)(PO₄)₃.0.16H₂O.

Median diameter (μm), maximum particle diameter (μm) and minimum inhibitory concentration (MIC, μg/ml) against Escherichia coli of the comparative silver based inorganic antibacterial agent were measured, and these results are shown in Table 1.

Comparative Example 4

To 40 g of a commercially available A-type zeolite, 1.2 g of silver nitrate in 450 ml of ion exchange water was added, and stirred at 60° C. for 2 hours to carry silver. Median diameter (μm), maximum particle diameter (μm) and minimum inhibitory concentration (MIC, μg/ml) against Escherichia coli of the comparative silver based inorganic antibacterial agent were measured, and these results are shown in Table 1.

TABLE 1 Maximum particle Median diameter diameter MIC Example 1 0.54 1.73 25 Example 2 0.51 1.51 50 Example 3 0.60 1.73 100 Example 4 0.57 1.98 100 Comparative 0.62 1.73 100 Example 1 Comparative 0.60 1.73 100 Example 2 Comparative 0.52 1.98 100 Example 3 Comparative 3.2 8.82 100 Example 4

Example 5 Evaluation on Molded Article

The silver based inorganic antibacterial agent obtained in Example 1 was blended at a concentration of 0.1% with a nylon 6 resin available from Ube Industries, Ltd., and injection-molded at 280° C. to obtain a molded product a which was a plate of 2 mm in thickness. The color difference ΔE immediately after molding between the molded product a and a molded plate which contained 0.1% of a zirconium phosphate obtained by the same procedure as in Example 1 except that no substitution with the silver was performed, was measured using a colorimeter. The results were shown in Table 2. The injection molded plate was immersed in a 0.1% sodium chloride solution at 90° C. for an hour and exposed to outdoor, and then the color difference ΔE thereof was measured using the colorimeter. The results are also shown in Table 2. Also, the injection-molded plate was used to conduct an antibacterial test in accordance with “JIS Z2801 5.2: Test methods for plastic products and the like”. The results of the obtained antibacterial activity are also shown in Table 2.

Similarly, molded products b-d and comparative molded products e-h were produced using the silver based inorganic antibacterial agents and the comparative silver based inorganic antibacterial agents produced in Examples 2-4 and Comparative Examples 1-4. The color difference and antibacterial activity of these molded products were also measured, and the results thereof are shown in Table 2.

TABLE 2 Color difference ΔE Antibacterial Immediately Immersion activity after in sodium Staphylococcus Escherichia molding chloride aureus coli Molded 0.2 3.2 More than 4.3 More than product a 6.1 (Example 1) Molded 0.3 2.8 More than 4.3 More than product b 6.1 (Example 2) Molded 0.1 1.9 More than 4.3 More than product c 6.1 (Example 3) Molded 0.4 2.2 More than 4.3 More than product d 6.1 (Example 4) Comparative 1.7 8.3 4.1 More than molded 6.1 product e (Comparative Example 1) Comparative 3.4 12.1 More than 4.3 More than molded 6.1 product f (Comparative Example 2) Comparative 6.9 9.3 More than 4.3 More than molded 6.1 product g (Comparative Example 3) Comparative 23.0 32.1 More than 4.3 More than molded 6.1 product h (Comparative Example 4)

Example 6 Nylon Spinning Test

The silver based inorganic antibacterial agent produced in Example 1 was blended at a concentration of 10 wt % with a nylon resin to produce a master batch. The master batch was mixed with nylon resin pellets to prepare an antibacterial resin containing the silver based inorganic antibacterial agent at a concentration of 0.15 wt %. Then, the antibacterial resin was melt-spun at the spinning temperature of 285° C. using a multi-filament spinning machine to obtain a nylon fiber (fiber a) containing the antibacterial agent with 24 filaments. Similarly, fibers b-d and comparative fibers e-h were produced using the comparative silver based inorganic antibacterial agents produced in Examples 2-4 and Comparative Examples 1-4. Yarn breakage during spinning, and the color difference ΔE of the product that had been washed three times were measured using the colorimeter. The results are shown in Table 3. The resulting nylon fiber containing the antibacterial agent was scoured and washed 3 times, and then antibacterial property was evaluated by a quantitative test in accordance with JIS L 1902⁻¹⁹⁹⁸ using Staphylococcus aureus and the results thereof were shown in Table 3.

TABLE 3 Yarn Antibacterial activity breakage ΔE After scouring After washing Fiber a None 1.8 More than 5.1 More than 5.1 (Example 1) Fiber b None 1.2 More than 5.1 More than 5.1 (Example 2) Fiber c None 0.9 More than 5.1 More than 5.1 (Example 3) Fiber d None 0.7 More than 5.1 More than 5.1 (Example 4) Comparative None 2.7 More than 5.1 More than 5.1 fiber e (Comparative Example 1) Comparative None 4.5 More than 5.1 More than 5.1 fiber f (Comparative Example 2) Comparative None 6.0 More than 5.1 More than 5.1 fiber g (Comparative Example 3) Comparative Some 8.8 More than 5.1 More than 5.1 fiber h (Comparative Example 4)

From these results, it is clear that the silver based inorganic antibacterial agent of the present invention is excellent in processability such as spinnability and also excellent in colorlessness when blended in the plastic products. In addition, better durability of the antibacterial effect was observed in the silver based inorganic antibacterial agents of the present invention compared with the existing silver based inorganic antibacterial agents.

Industrial Application

The novel silver based inorganic antibacterial agent of the present invention is excellent in processability by virtue of homogeneous and fine particles, and also excellent in colorlessness and antibacterial properties in plastic products. Therefore, it is an antibacterial agent having high applicability to fine fibers, paints and other applications in which processabilities is of importance. 

1. A silver based inorganic antibacterial agent comprising, as an effective ingredient, a compound represented by the following general formula (1): Ag_(a)Na_(b)H_(c)(H₃O)_(d)Zr_(e)Hf_(f)(PO₄)₃ .nH₂O  (1) wherein, in the general formula (1), a, b, c, d, e and f are positive numbers which satisfy 1.75<(e+f)<2.25 and a+b+c+d+4(e+f)=9, and n is not more than
 2. 2. The silver based inorganic antibacterial agent according to claim 1, which is obtained by allowing a compound represented by the following general formula (2): Ag_(a)Na_(b)H_(c1)Zr_(e)Hf_(f)(PO₄)₃  (2) wherein, in the general formula (2), a, b, c1, e and f are positive numbers which satisfy 1.75<(e+f)<2.25 and a+b+c1+4(e+f)=9, to absorb moisture.
 3. The silver based inorganic antibacterial agent according to claim 2, wherein the compound represented by the general formula (2) is obtained by ion-exchanging a zirconium phosphate compound represented by the following general formula (3): Na_(b1)A_(c1)Zr_(e)Hf_(f)(PO₄)₃ .nH₂O  (3) wherein, in the general formula (3), A is ammonium ion and/or hydrogen ion, b1, c1, e and f are positive numbers satisfying 1.75<(e+f)<2.25 and b1+c1+4(e+f)=9, with an aqueous solution containing silver nitrate in an amount of not less than 0.6b1 mol and not more than 0.99b1 mol per 1 mole of the above compound, followed by calcining.
 4. An antibacterial product containing the silver based inorganic antibacterial agent according to claim
 1. 